So how does the system work, does it automatically spray when the rpms are in the ideal range or does the driver have to manually press a button?

you can do either way. if you get a window switch, you can set it so the system doesn't start spraying until you hit a certain RPM and will shut off if you set it at the top end. for instance, you set it to start spraying at 3krpm and shut off at 6.5k rpm, if you wanted.